Furnace heated by high frequency coils



June 23, 1931. w. ROHN- 1,811,213

FURNACE HEATED BYIHIGITI FREQUENCY COILS Filed Jan. 7, 1930 Patented June 23,1931

WILHELM ROHN, OF HANAU-ON-THE-MAIN, GERMANY summon HEATED BY HIGH FREQUENCY COILS Application 111m :ruuuar 7,1930, Serial No. 419,151, and in Germany August s, 1927.

This invention relates to the coils of furnaces heated by high frequency electric currents, the use of which is increasingly warranted in carrying out metallurgical processes. In these furnaces it is highly de J sirable to strengthen the primary coil itself and to-fix it in so stable a manner that during tilting for the pur ose of pouring no bending or displacing o theseparate windin towards one another takes place. Re-

' in orcements of this kind have hitherto been effected by placing, for example, a double bar on the inside and outside of the coil, or by arranging a comb-shaped bar 011 5 one side of the 0011. In the first case a really stable support for each separate winding is not generally obtained, and in the second case there is a risk of the teeth of the bar of the concrete grooves can break and the asbestos crumbles in the course of time. Alw

sosupporting the coil on one side by wood 01 the like is not satisfactory.-

According to the present invention tha boil is strengthened by bars of electricall insulating material capable of withstan ing temperatures which arise, and which are 36 fixed by means of nuts or bolts onto ,bolts or nuts. These bolts or nuts are externally soldered onto the various turns of the coils and the bolts are arranged to pass through holes in the bars.

In order that the invention maybe clearly I understood and readily carriedinto' eflect some constructions affording an extremely eflicient reinforcing of the coil will be de-,

scribed with reference to the accompanying 4 drawings in which Figure 1 is a cross-section through a number of coil windings strengthened according to the present invention,

Figure 2 is a similar cross-section showing a modified form of the supporting bars,

Figure 3 is a side elevation showing the COIlIlGCtlOIlbGtWBBII two supporting bars,

Figure 4 is a central section on the line- As shown in Figure 1, headed screws or screw-threaded bolts 6 are soldered firmly to the outside of the separate coil windings a in a nearly radial direction. These screws can, for example, be made of brass. A bar '0 of an electrically insulating material capable of resisting the temperatures and mechanical stresses which arise, is pushed over the bolts and is fixed by means of nuts d. If the coil is made, for example, of copper tubes through which water flows, this to enbar can be made of Pertinax, an insulating material obtained by impregnating paper with artificial resin and pressing several sheets together with the application of heat, while for very high temperatures asbestos strip or mica is chosen. In this way the windings arerigidly connected one below the other and the connection remains fixed and serviceable despite the stresses due to the temperatures to which it is subjected.

If the reinforcing is to be made still firmer, a bar of brass or other metallic ma- --.ter,ial e can placed on the insulatin bar as shown in Figure 2, and insulating tu bes f can be arranged in the spaces between the metal bar and the bolts in order to revent arcing across the coil winding. Pre erably, a second tbar of insulating material 0 .is then placed against the metal bar.

some circumstances, for example, if large mechanical stresses arise in tilting, these vertically arrang "d insulating and metallic strips can withiadvantage be connected in pairs by a fastening plate 9 (see Figures 3', 4 and 5). These plates which need not extend over the whole length of the coil can, for example, be made of brass. In many cases it is advisable to employ chrome nickel as the material for the plates and bars, as this has a highrigidity with small conductivity .at high temperature. 5

Since the plates 9 have no considerable dimensions at right angles to the direction of the stresses and do not completely surround the coil, but only extend over a given angle, the currents induced in these plates have no appreciable disturbing effect.

In order that a furnacefurnished with such a coil can be tilted conveniently for the purpose of emptying, the plates 9 are provided with trunnions k and thus a rigid connection is obtained between the coil and the trunnions h which rest in hearings in the furnace support. Thus it becomes possible to connect the trunnions it absolutely rigidly with all the windings of the coil of the oven, so that in operation, and particularly in tilting, no undesirable stress or deformation is set up. The trunnions themselves are rotatably mounted in bearings fixed in the furnace supports and to this extent they are not completely rigid relatively to the furnace supports.

In the manufacture of the reinforcement described above it is preferable to push an iron template or former over the bolts, in place of the insulating bar, while the bolts are beingsoldered to the windings of the coil in order to fix the bolts in position. The band of insulating material can generally not be subjected without damage to the temperatures which arise in soldering. Now as the bolts are absolutely fixed in their right places by the soldering, it is occasionally difficult to withdraw the templates which had previously been placed in position. Because of this it may be advantageous to solder screw-threaded nuts in to the coil windings in place of screw-threaded bolts, and the bolts which carry the insulating bar can be screwed into these as' is shown in Figure 6. In this method of o eration it is possible to screw out the b0 ts after the soldering has been effected and to withdraw the templates without further difiiculty.

Preferably, a smaterial is chosen for the nuts such that it is not damaged by the heat during soldering, for example, a non-magnetic copper or nickel chrome alloy is suitable, while the bolts themselves can be made out of a metal or alloy, for example, brass, which has little resistance to heat, since in operation generally very strong heating does not take place.

If only the nuts and not the bolts are soldered a still further advantage is obtained which is particularly noticeable 7 when very valuable materials capable of resistip'g heat are em loyed. Bolts or nuts are ways produce from round material, and inthe manufacture of nuts relatively little loss of material arises during turning and screw cutting in comparison with that in the production of a screw-threaded bolt. -This savin in the lost material is of importance with alloys as for example, with non-magnetic chrome.

I claim 1. A strengthened coil nickel-copper or nickelfor a furnace heated by high frequency electric currents in which bars of electrically insulating material capable of withstanding the temperatures which arise are fixed to the coil by means of a nut-and-bolt connection, one element of the nut-and-bolt connection being externally soldered onto the various turns of the coil, and the bolts being passed through holes in the bars.

2. A coil according to claim 1 in which nuts are soldered onto the turns of the coil 30 and consist of a material which is not damaged by soldering, while the screw-threaded bolts are made from a material relatively i11- capable of withstanding high temperatures.

3. A coil according to claim 1 in which 35 bars of a metallic material are employed between the insulating bars to reinforce them and insulating tubes are placed in the holes through the bars so as to prevent a conductive connection being set up between the bolts.

4. A coil according" to claim 1 in which nuts are soldered on the turns of the coil" and consist of a material which is not damaged by soldering, while the screw-threaded.

bolts are made from a material relatively incapable of withstanding high temperatures, an bars of a metallic material are employed bet veen the insulating bars to reinforce them and insulating tubes are placed in the holes nection, one element of the nut-and-bolt connection being externally soldered on to the various turns of the coil, and the bolts being passed through holes in the bars which are in pairs connected by cross-strips.

6. A strengthened coil for a furnace heated by high frequency electric currents in which vertically arranged, bars of electrically insulating material capable of withstanding .the temperatures which arise are fixed to the coil by means of a nut-and-bolt connection, one element of the nut-and-bolt connection being externall soldered on to the various turns of the coi and the bolts being passed through holes in the bars which are in pairs connected by cross-strips, two opposite cross-strips being nions adapted to rest in nace support.

7 A strengthened coil for a furnace heatpzovided with trunarmgs 1n the fured by high frequency electric currents in high frequency electric currents in 105 which bars of electrically insulatingmaterial ca ble of withstandin the temperatures w 'ch' arise are fixed to t e coil by means of nuts soldered on to the various turns of the I coil and bolts passed through holes in the bars and screwed into the sand nuts.

8. The method of constructing coils for electric furnaces heated by hi h frequency currents which com rises pus 'ng an iron 10 former over a num r of screw threaded bolts, solderin the bolts to the various turns of the coil, an then replacing the iron former by an insulating bar.

In testimony whereof I afiix m si ature.

. WILHE R HN. 

